Rule of 720 - With Divisors

There is a clever extension to the Rule of 720 that is a bit easier to compute. Roger Taft explains and provides some examples. The KenKen solver is now capable of detecting it.

The rule is simple: If the Rule of 720 target product is not divisible by 2/3/4/5/6 then all 2s/3s/4s/5s/6s can be eliminated from each of the units that are unknown

This occurs most commonly with a 5, but cases with 3, 4, and 6 have been found.

In the first example the block is Rows A and B.
The target product is (720*720)/(15*240) = 144
This is not divisible by 5. So all 5s (shown in yellow) in the unknown units (boxed in blue) can be eliminated

In the second example the target block is columns 4, 5 and 6.
The target product is (720*720*720)/(90*12*12*72) = 400 which is not divisible by either 3 or 6. So there are many eliminations (shown in yellow) in the unknown units (boxed in blue)